The making of fiberglass

A READER IN WEST VIRGINIA, who says he’s new to boating, wants to know how fiberglass boats are made.  He has already discovered for himself that they’re not made from molded plastic, as he first thought.

Well, where to begin? Let’s stick with the hull.  Most production-run hulls are solid fiberglass built of this laminate: Alternating layers of chopped-strand fiberglass mat at 1.5 ounces to the square yard, and woven glass fiber roving at 24 ounces to the square yard.  These two layers are called a ply, and each ply is about 3/32 inch thick.  All the fiberglass is thoroughly saturated with polyester resin, which also glues the layers together into one solid mass.

This standard laminate weighs about 94 pounds a cubic foot and the glass fibers account for about 35 percent of the total weight.  It’s the glass fibers that add strength and flexibility to the laminate:  polyester resin on its own is not particularly strong and its rigidity tends to make it crack easily.  Together, the fiberglass and the resin combine their best qualities in a boatbuilding material that has stood the test of time.

Now, the glass fabrics most commonly used by boatbuilders are cloth, woven roving, and chopped strand mat.

Ø Cloth is thin and strong. It’s used for sheathing wood or as a finishing layer on a fiberglass laminate because it leaves a smooth finish.  It is not usually used to build up the hull laminates.

Ø Woven roving has a loose weave with a rough finish. It provides strength but is usually topped with cloth or mat to make it fair.

Ø Chopped strand mat comprises short strands of glass fibers laid flat in random fashion and held in place by a sizing that is soluble in the right kind of resin.  It’s the weakest of these three fabrics, but it bonds well.  In repair work, chopped strand mat is the fabric first applied to old fiberglass, to ensure a good strong bond between the old and the new.

In a way, resin and fiberglass are the marine equivalent of bricks made of mud plus straw, or concrete plus steel reinforcing bar.  The resulting product shows characteristics greater than the sum of its components taken separately.

There are many tricks and wrinkles known to those who work with fiberglass on a professional basis, of course, but for beginning sailors in West Virginia, this is about all they need to know for now.

Today’s Thought

The glory of a workman, still more of a master-workman, that he does his work well, ought to be his most precious possession; like the “honour of a soldier,” dearer to him than life.
— Carlyle, Essays: Shooting Niagara

Tailpiece

People who think they know everything seldom seem to realize how much they irritate those of us who actually do.

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)